build: Properly apply modes in meson_post_install.py
In our environment, the default umask is 0o022
so the g+w
permission
is missing from the packaged icons
directory.
Manipulate the umask to match the modes we want.
We can't just use 0
for everything because makedirs
always uses
0o777
for parent directories since Python 3.7. We also want to
keep /var/lib
at 0o755
.